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5-12-2015
Investigation of Asymmetric Impacts on ProtectiveHeadgearKristina MederoWestern Kentucky University, [email protected]
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INVESTIGATION OF ASYMMETRIC IMPACTS ON PROTECTIVE HEAD GEAR
A Capstone Experience/Thesis Project
Presented in Partial Fulfillment of the Requirements for
the Degree Bachelor of Science with
Honors College Graduate Distinction at Western Kentucky University
By
Kristina Medero
*****
Western Kentucky University
2015
CE/T Committee:
Approved by
Dr. Edward Kintzel, Advisor
______________________
Dr. Doug Harper Advisor
Dept. of Physics and Astronomy
Ami Carter
Copyright by
Kristina Medero
2015
ii
ABSTRACT
This project explores helmet-to-helmet impacts and their detriments with a unique
perspective. The propagation of dangerous waves into the brain can result in a
concussion. Considering 60% of NFL players have had at least one concussion (Epstein
2011), it is imperative to understand the materials that construct helmets and observe how
these materials behave in regards to impact location while recording wave propagations
from the impacts. This study interrogates the effect of asymmetric impacts on gridiron
football helmets using the Large Chamber Scanning Electron Microscope (LC-SEM).
Utilizing two standard issued football helmets made of polycarbonates, a hard plastic,
vibrations from a controlled impacted recorded by accelerometers placed along the shell
of the helmet measured waves of ±4g force. The frontal impact recordings depicted
higher single peaks, while side impacts revealed vibrational relatively lower peaks. To
investigate the response of the helmet material to collisions, helmet impacts were carried
out in air using a specific pendulum apparatus (to simulate the collisions) and 179 N of
force. It was subsequently studied in the LC-SEM and the images depicted clear damage
to the helmet shell. Ultimately, this project seeks to provide aid in the endeavor of
concussion prevention headgear.
Keywords: Helmet, Collision, Concussion, Waves, Accelerometer, Microscope
iii
Dedicated to
Jace Lux
iv
ACKNOWLEDGEMENTS
This project would have been impossible if not for assistance from Dr. Doug
Harper and guidance from Dr. Edward Kintzel. Dr. Kintzel provided the tools necessary
to conduct analysis of the football-helmets’ degrading integrity after multiple collisions.
Without a working program to collect and analyze data on LabView conclusions could
not have been drawn. Dr. Harper provided the MyRio and programming to conduct the
project, and therefore I extend a great amount of gratitude to Dr. Harper for his
impeccable leadership and inspiring technological work. Also, appreciation must go to
the Nondestructive Analysis (NOVA) Center, which provided the necessary equipment to
complete this project. Dr. Kintzel and the NOVA Center provided flexible hours to fit my
hectic schedule. Without access to facility collecting data would have been for more
tedious. Finally, the Faculty Undergraduate Student Engagement scholarship and the
Honors College contributed funding to both conduct and present research throughout the
process of developing data. I send my greatest regards to their assistance and assurance in
my abilities to produce highly competent and scientific work.
v
VITA
October 1, 1992…………………………………………………Born – Plantation, Florida
2011……………………………………………………….....…Nova High School, Davie,
Florida
2013………………………………………………… Research Assistant at NOVA Center
2013……………………………………………….…Physics Tutor and Teacher Assistant
Western Kentucky University
2013………………...……………………………….….……WKU FUSE Grant Recipient
2013…………………………………....……Poster presentation at SESAPS 2013 (WKU)
Fall 2014………………………………………. Kentucky Honors Round Table Presenter
Fall 2014…………………………...WKU 10th
Anniversary Biological Preserver Speaker
FIELDS OF STUDY
Major Field: Health Sciences
Minor Field: Biology
vi
TABLE OF CONTENTS
Page
Abstract……………………………………………………………………………………ii
Dedication………………………………………………………………………………...iii
Acknowledgements……………………………………………………………………….iv
Vita………………………………………………………………………………………...v
List of Figures……………………………………………………………………………vii
Chapters:
1. Introduction………………………………………………………………………1
2. Methods…………………………………………………………………………..5
3. Results and Discussion……………………………………………………....….14
4. Conclusion…...………………………………………………………………….18
References…….…….………………………………………………………………..…..20
vii
LIST OF FIGURES
Figure Page
Figure 1…………..……………………………………………………….………….…....6
Figure 2a-b...………………………………………………………..…….…………….…8
Figure 3………………………………………………………………..….…………….....9
Figure 4………………………………………………………………..….……………...10
Figure 5………………………………………………………………....………………..11
Figure 6…………………………………………………………………………………..12
Figure 7…………………………………………………………………………………..14
Figure 8…………………………………………………………………………………..15
Figure 9…………………………………………………………………………………..16
Figure 10…………………………………………………………………………………17
1
CHAPTER 1
INTRODUCTION
The game of football stems as far back as 2500 BCE, and expanded from areas of
Asia (Britannica Encyclopedia). Eventually it reached America in the 1880’s, but didn’t
gain popularity until after World War II when John Thorpe developed the National
Football league. The evolution of the football helmet follows the establishment of the
game into American pop culture. As it grew in popularity, it also became exponentially
more violent. Helmets started as simple leather padding to prevent injury, but in actuality
gave little protection. It wasn’t until 1940 when the more modern plastic football helmets
with a chin strap facemask were developed and patented by the John T. Riddell
Company, which has reduced deaths by nearly 70 % (Levy 2004). These football helmets
are the center of the study and focus on how well they actually protect athletes from
concussion. Dr. Lawrence M. Lewis and associates note in their study “Do Football
Helmets Reduce Acceleration of Impact in Blunt Head Injuries?” that helmets do in fact
reduce the force peak of an impact (2008). However, experts debate the extent of
protection.
For decades, multiple efforts developing better helmets for players have
consumed the sport industry, especially, concerning concussion prevention. Riddell,
2
major contributor of protective gear in the NFL (Riddell 2015), has advertised their
attempts to create head that prevents concussions. In fact, in 2002 the University of
Pittsburg Medical revealed that the company developed a helmet that would reduce
concussions by 31% (Iverson 2006). However, this conclusion proved unsupported by
the data and Riddell had to retract their statement. Even with the ban of helmet-to-helmet
collisions of defenseless players, just a couple of years ago New Orleans Saints became
under scrutiny for a bounty system for injuring other players (Coffey, 2012).
As a result, the National Football League (NFL) has received attention recently
for not providing the necessary protective gear for its athletes. Studies suggest while a
slight decrease in concussions does occur, in professional leagues, concussions are still a
significant issue (Lewis 2008). While, concussion research has included a variety of
techniques to decrease injury, our current project provides a unique perspective to assist
in identifying ways to mitigate concussions due to multiple collisions. This project seeks
to interrogate the effect of asymmetric impacts on gridiron football helmets using
simulated impacts in combination with the imaging capabilities of the Large Chamber
Scanning Electron Microscope (LC-SEM). Current helmet technology produces
protective headgear that can withstand about 548 pounds of force (Riddell 2015). As new
materials for these protective systems are developed, the ability to predict and test in
“near real world” situations are key to maximum protection of the athlete.
During a helmet-to-helmet collision, vibrations from the impact propagate on the
surface of the protective headgear in a complex fashion. The materials that comprise the
headgear must maintain their integrity after multiple acute stress conditions. Current
3
headgear architectures still allow for the transmission of dangerous waves into the brain
resulting in the damage and destruction of thread-like fibers in the arachnoid, a protective
layer around the brain that is meant to keep it secure. When the fibers are broken, the
brain shifts. The effect is seen as a concussion; when the head experiences a sudden jolt
and soft tissue in the brain moves in reaction to the sudden force (Web-Md 2013). This
sudden force alters brain cells and results in the release of all neurotransmitters in an
unhealthy cascade, flooding the brain with chemicals and dulling receptors linked to
learning and memory.
Immediately after injury, an individual may experience confusion and
disorientation, along with nausea and blurred vision. While many symptoms appear
instantly, others may not surface for weeks. Delayed symptoms tend to be more drastic,
including changes in behavior, such as aggressive tendencies, paranoia and suicidal
tendencies (Web-Md 2013). On the college level 34% of players have had at least one
concussion, and 20% have had multiple. By the time a player reaches the NFL more than
60% of the players will have at least one concussion, and 45.7% will endure multiple
concussions (Ebstein 2011). When an individual experiences multiple concussions it may
ultimately result in degenerative brain diseases, such as Parkinson's Disease, Lewy Body
dementia, or Alzheimer's Disease (Web-MD 2013). A fundamental understanding of the
materials that construct the helmet, how these materials behave over time, and their
ability to mitigate transmission of waves into the brain is obligatory. A strategy rooted in
science can then be developed to reduce injuries and aide in developing novel materials
and helmet architectures from these helmet-to-helmet collisions.
4
In 2013, the Baltimore Ravens in the Super Bowl used the new Xenith helmet
manufactured in Lowell, MA. This helmet varies from the more common Riddell helmet
because it advertises an inflatable padding and thermoplastic material, rather than a
standard polycarbonate plastic, which the company suggests can adapt with dependency
on the collision (Xenith 2013). With new innovated models developing it is imperative to
look at more unique perspectives of analyzing helmets. The LC-SEM provides real-space
imaging to track minor changes in the surface morphology on the helmet that may result
in diminished protective capacity. This initial study has the potential to contribute to the
advancement of sports medicine in its endeavors to decrease the occurrences of
concussions inflicted on football players and may provide a blueprint for other headgear
technology. Currently, polycarbonate plastics are the main materials being used by the
companies providing the NFL with protective headgear. In an effort to provide increased
safety for its players, the NFL has called for a well-rounded comprehensive investigation
into the role these and other novel materials play. Since shock waves on impact cause the
concussion, this project may be used for future studies to evaluate the best method for
wave suppression in the development of enhanced helmet architectures.
5
CHAPTER 2
METHODS
To investigate the response of each helmet material to a collision, helmet impacts
were carried out in air using a specific pendulum apparatus (to simulate the real-life
collisions). Before and after collision changes were observed in the LC-SEM; however
the collision waves from the pendulum apparatus was not measured with the
accelerometers. The experimental setup, however, did not allow for a precise impact
location. Real-space imaging of the surface of the polycarbonate helmet at the impact
site(s) were carried out nondestructively using the LC-SEM using backscattered electrons
(BSE). Since the helmets are non-conductive the LC-SEM operated in variable pressure
mode was needed to carry out the experiment. The benefit in using this mode is not
requiring to sputter-coat the surface of the helmet in a conducting medium to facilitate
imaging of the surface.
Initially, the helmet was imaged prior to impact using the LC-SEM to evaluate the
morphology of the surface prior to being subjected to impact. To study the change in
surface morphology, the previously scanned helmet was secured to a platform. A second
helmet of the same model and size was hung from the pendulum apparatus and filled with
40 lb (18.2 kg) of lead masses in order to mimic the force of a real-life collision. Lifting
the weighted helmet about a meter and half from the ground provided the necessary
6
assistance of gravitational force to create 179N to impact the helmet. These calculations
of force were identified as such:
Force of Impact= Force of Gravity= mg= (18.2 kg)(9.81m/s2)= 179 N
Where m is the mass of the weighted helmet and g is the acceleration of gravity.
This process was repeated several times along the same impact location. Changes in
surface morphology were observed by scanning the helmet a second time using the same
backscatter electrons in variable pressure mode conditions. The image was used to
identify grooves, scratches, and dents in the helmet.
The same standard issued Riddell football helmets made of polycarbonates was
used to measure vibrations from a controlled impact with accelerometers placed along the
exterior of the helmet approximately 2.54 cm apart Figure 1.
Accelerometers monitoring the vibrations from a controlled impact were used to
study the evolution of the wave as it traveled on the surface of the helmet. The
accelerometers from Digilent Inc., were model number PmodACL and are 3-axis
accelerometer modules powered by an Analog Devices ADXL345 accelerometer chip.
Figure 1. Image of helmets depicting transverse and longitudinal graphing
of the accelerometers placement.
7
For our application the I2C controller mode was used for communication. Since the
devices only supported two separate I2C addresses, the addresses were set via software
using the digital outputs of the myRIO to communicate with more than one
accelerometer. The accelerometer that was to be queried was set to one of the available
addresses and the other accelerometers were set to the alternate address. This process
continued rapidly cycling through each accelerometer. Accelerometers were placed in
longitudinal and transverse directions relative to the front of the helmet. The positions
chosen as the frontal and side impacts are the most common areas of impact, and are
therefore ideal for this research (Pellman 2003).
Data collection was carried out using custom designed LabView software, which
measures acceleration in terms of g (9.81 m/s2) along a time line of 3-10 seconds for each
impact. The accelerometers depicted in Figure 2a-b recorded the frequency of wave form
data in versus time, which was determined by the sample rate (1/sample rate). Recorded
vibrations were used to observe the differences of frontal versus side impacts on headgear
by the measuring the manner in which the impact waves propagated about the helmet.
Figure 2 a. Accelerometers used for recording
waves
Figure 2 b. example of frontal placement
along the shell
8
The MyRio device interfaced to the computer and the three accelerometers. The
LabView 2014 32-bit program was used for this study is depicted in Figure 3. Three
second intervals were selected for the duration of 3 seconds, and the resolution was set to
± 4g to measure the smaller impact and the waves that propagated along the surface of
the helmet. The run arrow was pressed and the waves were measured using
accelerometers. While they recorded waves in the x, y, and z coordinates, only z was
used for analysis because these waves enters the cranial space. In other words, these
waves interact with the brain and fibers securing it while x and y are tangent to the
helmet. After the duration concluded a the data was saved onto a thumb drive connected
to the MyRIO under a file labeled “acceleration data.”
To develop an understanding of the manner in which the wave propagates along
the surface of the helmet, a method was developed using smaller impact forces. The
Figure 3. MyRio screen with arrow pointing to “Run”, which was used to record the data
depicting 10 second duration with ±4g resolution
9
advantage of this was to proceed in a more controlled way and to generate similar impact
waves every time. To accomplish this, a small hammer was used on two selected
locations on the surface of the helmet. The impact locations were selected based on the
most common areas of impact recorded amongst football in-game collisions (Pellman
2003). They were isolated and kept constant by securing a small blunt tip to the helmet as
demonstrated by Figure 4.
The waves were measured using three accelerometers (A, B, C). One
accelerometer (A) was located directly adjacent to the impact sight to record initial wave
that would be produced by the impact. The second accelerometer (B) was placed to the
right of the impact sight and the last one (C) was placed to the left. Each recorded various
locations in a systematic way along the indicated points, as displayed in the image in
Figure 3 above. A sample of accelerometer data of the frontal impact point is displayed in
Figure 5 in terms of g (9.81 m/s2) versus time. Multiple impacts were carried out along
Figure 4. Small blunt flat tipped screw head and hammer used to create specific
impact sight for testing.
10
lines of the shell and the subsequent raw data was averaged to reduce error from unequal
impacts using equation 1 and combined on one graph as displayed in Figure 6.
Average Peaks = ∑initial impact peaks/ # of impacts Equation 1
-1
-0.5
0
0.5
1
1.5
2
1
52
10
3
15
4
20
5
25
6
30
7
35
8
40
9
46
0
51
1
56
2
61
3
66
4
71
5
76
6
81
7
86
8
91
9
97
0
Forc
e (
g)
Time (1/sample rate)
MyRIO Recording of One Impact
A - X
A - Y
A - Z
B - X
B - Y
B - Z
C - X
C - Y
C - Z
Figure 5. Single impact recording from the MyRIO. It recorded waves in the x, y, and z coordinates
from accelerometers A,B, and C.
11
Fig
ure
6.
Gra
phed
pea
ks
of
Raw
Co
mb
ined
Dat
a al
ong l
ong
itud
inal
line
A i
n t
erm
s o
f g/s
. A
-Z i
s th
e in
itia
l im
pac
t p
oin
t.
Po
ints
B-Z
(1
-14
) ar
e th
e te
sted
po
ints
alo
ng t
he
lon
git
ud
inal
line
of
row
A o
n t
he
hel
met
.
Tim
e (1
/sam
ple
rat
e)
12
Clearly from figure 6 the data is difficult to interrupt in terms of time. Therefore,
the data was set to relative distance from the impact point to illustrate change in
amplitude as the wave propagated along the shell. The impacts were tested five times and
the data were normalized to equation 2 to remove potential difference in force of impact.
Where I stands for relative intensity of the amplitude and g is the 9.81m/s2 the device was
recording. The maximum g recorded was 2.38 g and this value was used to standardize
the data in a way to compare wave intensities between frontal and side impacts.
Multiplying by ten standardized the data further to make reading comparisons easier
without skewing the results.
I= (g of point/2.38g) * 10 Equation 2
Each impact was record using LabView and converted to Excel Word program for
analysis. The data of each point set was combined in a three dimensional graph to present
change of intensity over distance away from the initial impact point on the helmets
exterior and is recorded in the result section below.
13
CHAPTER 3
RESULTS AND DISCUSSION
Images of the helmets, before and after multiple collisions reveal changes in
morphology of the polycarbonate materials. Figure 7 below illustrates a helmet before
impact with minor imperfections on the shell of the helmet. After multiple impacts
imaging from the LC-SEM provides evidence of damage to the surface of the helmet
Figure 8. The damages viewed suggest possible diminished protective capacity. The
damage is localized; therefore the impact does not significantly propagate along the
surface of the helmet to divert impact away from the brain.
Figure 7. Minor defects observed on helmet before multiple impacts
14
Choosing the most likely impact points, three accelerometers recorded wave
propagation and readings were amalgamated to track total progression throughout the
helmet. Figure 9 below demonstrates the progression of a single impact after data was
standardized for the frontal propagation of the helmet in terms of intensity versus
distance away from initial impact point. The Z axis on the graph represents the position
the accelerometer had on the helmet grid. The legend (1-14) also represents the position
on the grid in reference to figure 1. As expected the curve follows the shell of the helmet
traced by the red line. Figure 10 includes the z-axis to reveal position along the helmet is
curved. The graph reveals relatively high single peaks of waves along the surface of the
helmet with damp lower peaks going into the helmet. This suggests some deterring of
waves acting within the cranial space. The graph also indicates the highest peak
Figure 8. Observed damage of helmet surface after multiple impacts
15
presenting itself directly behind the head from the frontal impact. When the waves travel
along the helmet shell they combine behind the head into one large peak.
The side propagations demonstrate more of a vibrational pattern as opposed to the
frontal single peak impact waves as observed in Figure 10. The graph is also represented
in a similar way to figure 9; where the Z-axis of the graph demonstrates its position on
the helmet grid referring to the transverse lines. This could result in more waves
interacting with brain. However, the peaks are relatively lower when compared to the
frontal impact. Therefore, while more chance for waves causing a concussion, they are of
a lower intensity. Perhaps this will lessen the impact of the overall injury. Similar to the
frontal impact the side impact resulted in a higher wave peak on the opposing side of the
initial impact. Identifying ways to prevent this effect could prevent future injury.
Figure 9. Standardized data of frontal impact propagation of plots along the A longitudinal line.
Position on helmet
16
Overall, the data reveal that despite efforts to prevent concussions wave
propagation and vibrational patterns were still observed along the shell of the helmet.
Side impacts have lower intensity reading, but more vibrational peaks, while frontal
impacts have higher single peaks. The LC-SEM reveals clear damage to the surface of
the helmet after multiple impacts. How this may mitigate or intensify the wave peaks.
Since this comparison is unclear, these findings could provide a basis for future
perspectives of analysis.
Figure 10. Side impact standardized data of transverse plots along the G line on the helmet.
Position on helmet
17
CHAPTER 4
CONCLUSION
The results of this investigation are a first step in developing a sound basis for
further measurements and could provide new insights into the construction of improved
protective headgear in sports. This has the potential to impact the medical community, as
a more thorough understanding into the nature of the materials of protective headgear is
explored. Comprehension of the manner in which the brain is impacted after multiple
collisions is pertinent to concussion prevention. Accelerometers monitoring the vibrations
from a controlled impact should be used to study the evolution of the wave developed on
helmets after collisions. However, this strategy can be expanded to new experiments for
even more clear conclusions.
For example, as an approximation, an artificial “brain” can be constructed of Jell-
O (or similar) surrounded by a sealed flexible latex membrane (similar to a water
balloon) to further study the effects on the brain specifically. Accelerometers should be
placed on longitudinal and transverse directions relative to the front of the helmet, as well
as on a dummy-head or other head like structure with the simulated brain on the inside.
Recorded vibrations can be used to study the manner in which the impact waves are
propagated within the brain to better understand concussion prevention. Recording how
18
the waves interact with the cranial space specifically could result in more conclusive
research.
Further, studies using a more controlled impact mechanism should be used to
develop more meaningful results. The studies used for research in this report illustrated
an impact rod mechanism that provided impacts with less differentiation in force. More
controlled force would further limit error in experimental data. However, the limitation of
resources prevented this technique for being utilized here. Also, studying wave
differentiation before and after multiple impacts occur could result in a better
understanding of the overall integrity of a helmet. As the helmet endures more impactful
waves, understanding wave propagation in regards to change in morphology could give
more empirical results on when to replace equipment. Also the utilization of more
accelerometers along the helmet could provide solidified data with less margin of
uncertainty.
Finally, comparing the impact waves on the Xenith helmet could provide insight
into which material is better to use. The new Xenith helmet manufactured in Lowell, MA
should also be tested to compare the inflatable padding and thermoplastic material that
can adapt with dependency on the collision (Xenith 2014). This helmet architecture is
similar to air bag use in cars. This will theoretically slow down the impact and reduce the
force felt by the head. Studying the differences in the architecture between Xenith and
Riddell should be researched. Overall, this experiment is successful in tracking the
change in wave prorogation and provides a novel perspective for observing helmet-to-
helmet collision.
19
REFERENCES
Coffey, W. (2012, March 5). NFL needs to start cleaning up ‘BountyGate’ by going after
Sean Payton and Gregg Williams for role in Saints’ bounty system. Retrieved
January 1, 2013, from http://www.nydailynews.com/sports/football/nfl-start
cleaning-bountygate-sean-payton-gregg-williams-role-saints-bounty-system
article-1.1032536
"Concussion: Causes, Symptoms, Diagnosis, Treatment, and Prevention." WebMD-
Better Information. Better Health. Web. 30. October. 2013.
<http://www.webmd.com/brain/tc/traumatic-brain-injury-concussion-overview>.
Ebstein, N. (2011). He NFL’s Big Problem: Concussions and What We Can Do To
Prevent Them.
Football Helmets, Shoulder Pads, Facemasks | Xenith. (n.d.). Retrieved April 28, 2014,
from http://shop.xenith.com/
Levy, Michael L., Burak M. Ozgur, Cherisse Berry, Henry E. Aryan, and Michael L.j.
Apuzzo. "Birth and Evolution of the Football Helmet." Neurosurgery 55.3 (2004):
656-62. Web.
Lewis, Lawrence M., Rosanne Naunheim, John Standeven, Carl Lauryssen, Chris
Richter, and Brian Jeffords. "Do Football Helmets Reduce Acceleration of Impact
20
in Blunt Head Injuries?" Academic Emergency Medicine 8.6 (2001): 604-09.
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Oriard, Michael. "History of American Football." Britannica. Print.
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